For example, as disclosed in the Japanese Patent Laid-Open No. 2003-134795, some of the prior art inverter systems are known to incorporate a temperature detecting element arranged inside the semiconductor device of an inverter system and to measure the temperature rise at the time of inverter startup; wherein, if the reading fails to conform to the reference level, the semiconductor device, hence the inverter, is evaluated as having an error, with the result that the inverter system is suspended.